Conventional x-ray sources generate the x-ray by using electron beam to excite an anode to generate x-ray emissions. Almost all of the power of the electron beam (e.g. 99%) is converted to heat in the process. A specific power density of 1 W/μm2 and a total power of 100 W are typical specifications for anodes of state of the art stationary micro-focus x-ray tubes. In micro-focus x-ray tubes, the area of the anode hit by the electron beam (the focal spot) is very small, on the order of tens of microns, to achieve a small source size for high-resolution x-ray imaging. The amount of heat generated can be spread to a volume of about 1 mm3 of the anode by metal thermal conduction mechanism without melting the center of the anode. However, the blackbody radiation rate alone on the surface of this small volume is not enough to radiate out this power to the outside radiation absorber cooled by water or air. Heat conduction to a larger area of radiation has to go through a long metal thermal conduction pass, which cannot transfer the amount of heat without causing significant temperature rise which can melt the spot hit by the electron beam. A rotating anode allows the heat to be distributed on a much larger area to avoid melting the anode. A specific power density of 2×10−2 W/μm2 and a total power of 10 kW are typical specifications for a state of the art rotating anode. For the same reason, the power density cannot be further increased for desired higher x-ray brilliance. Most conventional devices apply liquid convection methods (including liquid metal and water) to cool the anode. However, liquid convection heat exchange coefficient is not high enough to transfer the amount of heat without causing significant temperature rise that can melt the spot hit by the electron beam.